1. Field of the Invention.
The present invention relates generally to methods of manufacturing multiple-pane sealed glazing units and particularly to methods of manufacturing multiple-pane sealed glazing units having an insulating, flexible spacing-and-sealing assembly.
2. Description of the Prior Art
Sealed glazing units generally consist of two or more parallel sheets of glass which are spaced apart from each other and which have the space between the panes sealed along the peripheries of the panes to enclose an air space between them. Spacer bars are placed along the periphery of the space between the two panes and these spacer bars are typically long hollow perforated-metal sections, usually made from an aluminum alloy and fabricated either in the form of an extrusion or by rolling from flat-strip material. The hollow interior of the spacer contains desiccant material which is used to adsorb any residual moisture that may be in the enclosed air and to remove and additional moisture that may enter in the sealed unit air and to remove any additional moisture that may enter in the sealed unit over of a period of time. Typically, the spacers are assembled into a rectangular frame using corner keys. To fabricate the sealed glazing unit, the outward-facing channel between the spacer and glazing sheets is filled with either a thermosetting sealant such as polysulphide, silicone and polyurethane or a thermoplastic sealant such as butyl. There are drawbacks to both types of sealants.
One drawback with thermosetting sealants is that they are generally more permeable to gas and moisture vapour than the thermoplastic sealants. A second drawback is that thermosetting sealants must be cured before the units can be shipped and unless the curing process is specifically accelerated by heat, the units must be stored for at least a few hours before shipping. A third drawback is that during the curing process, thermosetting sealants typically outgas chemical vapours which may condense on the glazing sheets unless special measures are taken to adsorb the solvent vapours. This problem of outgassing is a particular concern for sealed units incorporating low-emissivity(low-e) coatings as the condensed chemical vapours may damage the sensitive optical thin-film coatings.
There are different problems with thermoplastic sealants. One drawback is that thermoplastic sealants do not typically form a chemical or structural bond with the glass and as a result, there are potential problems of spacer bar migration, cold creep and poor peel adhesion at cold temperatures. A second problem is that because the thermoplastic sealant rapidly cools down after extrusion from the hot-melt gun, the bonding process is almost instanteous and cannot easily be controlled. A third drawback is that during production of the sealed units, the sealant gunning pressure of the thermoplastic sealant is difficult to control and special measures must be taken to prevent the spacer frame and glazing sheets from shifting in position.
One way of overcoming these drawbacks with both thermosetting and thermoplastic sealants is to combine both types of sealants in a dual-seal design. For a conventional dual-seal design, there is an inner thermoplastic seal which functions as the prime moisture vapour and gas barrier seal and an outer thermosetting seal which functions as the structural adhesive seal. Typically, the production method for dual-seal units involves first laying down the inner seal which is a bead of polyisobutylene sealant on to the sides of the spacer adjacent to the glass sheets. The spacer frame is then placed between the panes and heat and/or pressure is applied to ensure that the polyisobutylene bead is compressed and fully wets out onto the surface of the glass. For the second outer structural seal, a thermosetting sealant such as silicone, polyurethane or polysulphide is used and is applied in the outward-facing perimeter channel between the two glass sheets. Dual-seal designs are commonly used for automated production lines where the inner seal also functions as a temporary adhesive to hold the glass sheets in position during the production process while the outer sealant cures. Dual-seal designs also potentially simplify the production process for gas-filling sealed units as the units can be gas-filled prior to the application of the outer sealant.
With a conventional edge seal design, there is significant perimeter heat loss through the conductive metal spacer. To improve the energy efficiency of the glazing unit, various efforts have been made in the past to fabricate the spacer from low-conductive plastic materials. However, the use of a plastic spacer accentuates technical problems relating to the integrity of the edge seal and also complicates the production process of the sealed units. As a result of these technical problems, none of these prior efforts to develop an insulating spacer has as yet been successfully commericalised in North America. In particular, none of the insulating spacers is suitable for flush glazing or structural glazing applications where durable but permeable silicone sealant is used to structurally bond the exterior glazing to the interior glazing and the interior glazing to the building structure. A further concern with plastic spacers is the problem of outgassing which for high thermal performance sealed units is compounded by the need to use only 3A molecular-sieve material in order to avoid the problem of low-temperature gas adsorption by larger-pore desiccant material.
Specific issues and problems raised by the prior art are reviewed below with specific emphasis on methods of manufacturing multiple-glazed sealed units with an insulating, flexible spacing-and-sealing assembly.
U.S. Pat. No. 3,758,996 issued to Bowser describes the addition of desiccant material as a fill to a flexible but solid plastic spacer strip. The plastic spacer strip is backed by a layer of moisture-resistant sealant typically thermoplastic butyl which extends across the spacer from the peripheral edge of one sheet of glazing to the peripheral edge of the other. The plastic spacer strip may be adhered to the glazing sheets with a cureable rubber adhesive but the spacer must be held in position until the adhesive is cured and this slows down and complicates the production process.
U.S. Pat. No. 4,193,236 issued to Mazzoni et al describes the use of separate adhesive cleats to prevent spacer bar migration in units where hot-melt butyl is used as the outer sealant. As with the use of conventional thermosetting sealants, one drawback of the cleat system is that there is a delay before the sealant cleats are cured and the glazing sheets are firmly held in position.
U.S. Pat. Nos. 4,226,063 and 4,205,104 issued to Chenel describes the use of a flexible dual-seal, spacing-and-sealing assembly comprising silicone sealant as the outer structural seal and desiccant-filled butyl sealant as the inner moisture vapour and gas seal. A major drawback of this type of edge seal design is that because the desiccant fill is contained within the low-permeable butyl sealant, moisture vapour is removed very slowly from the airspace.
U.S. Pat. No. 4,662,249 issued to Bowser overcomes the problem of slow moisture-vapour removal by reversing the two sealant materials so that the hot-melt butyl sealant is the outer moisture vapour and gas seal and desiccant-filled silicone sealant is the inner structural adhesive seal. A major drawback of this reverse dual-seal design is that very complex production equipment is required to hold the glazing sheets in position while the inner sealant cures. An additional problem is that a large amount of chemical vapours are released while the inner silicone sealant cures and this outgassing cannot escape and may condense on the glass sheets. As previously explaned where a low-e coating is incorporated in the sealed-unit, these condensed chemical vapours can potentially damage the sensitive coating. A further concern is that the addition of the desiccant-fill material reduces the adhesive strength of the structural bond between the spacer and the glazing sheets.
U.S. Pat. No. 4,335,166 issued to Lizardo et al describes a method of manufacturing a sealed glazing unit incorporating a heat-shrinkable plastic film located between two outer glass sheets and which is typically surface coated with a low-e coating. The flexible film is supported between two spacers and is held in position by the outer sealant which is typically polyurethane sealant. One concern is that over time the sealant material may creep and because the spacers are not structurally bonded to the glazing layers, the spacers may migrate inwards creating wrinkles in the flexible film.
The problem of perimeter heat loss has been addressed by prior work carried out by the inventors and has involved the development of a resilient spacing-and-sealing assembly consisting of a flexible foam insulating inner spacer and a low-permeable outer sealant. The inner spacer is typically backed by a high-performance vapour and gas barrier film and is made from moisture-permeable flexible or semi-rigid foam which contains a high percentage weight of desiccant-fill material. In fabricating the sealed unit, the flexible edge strip is laid down around the perimeter of the glazing sheets and is held in place by preapplied, pressure-sensitive adhesive on the spacer sides.
To a large extent, this use of the pressure sensitive adhesive on the spacer sides minimizes the traditional drawbacks of using thermoplastic sealants. However, conventional pressure sensitive adhesives do not form a strong chemical bond with the glass and as a result, there are possible long term durability problems because the glazing sheets may not remain structurally held together. Also, because there is no permanent structural bond, the flexible spacer-and-sealing assembly cannot be used for structural glazing applications.